The child object of a mirror will have "history" applied to it and remain a "Mirror" of the parent object. You can either disable history on the child object, or perform some kind of edit to it (like move it) to break the history.

Hi s7r83dg3, yup like Burr mentions that is not a bug, that is the history feature kicking in and updating the mirrored copy in response to changes in the original.

To turn it off, select the mirrored copy (the newer created object), and run the Edit > History command, which is here:



And then pick the "Disable update" option that shows up here:



- Michael